In an image sensor, an image signal including image information is generated by each pixel circuit. The image signals generated by each pixel circuit are delivered to an analog-to-digital converter (ADC) in order for digital conversion.
However, coupling occurs between a global signal for controlling a device such as an ADC and an image signal delivered from each pixel circuit, so that distortion may occur in the global signal. This effect is shown in FIG. 1.
FIG. 1 is a view when distortion occurs in a global signal and an output signal based on an input signal, in the case that the global signal is used to control a plurality of devices.
For example, if a device whose operation is controlled in response to a global signal is an ADC, a signal inputted into the ADC can be an image signal delivered from the pixel circuit. The image signal delivered from the pixel circuits may be signals (i.e., a falling edge) representing bright light and signals representing dark light. That is, image signals inputted into an ADC include signals having a large signal width and signals having a small signal width.
For example, when a signal 11 including information on a bright image has a falling edge and its signal width is large, a coupling capacitor is formed between global signals input to an ADC device. Also, due to such a coupling capacitor, distortion may occur in a global signal and also an input signal 22. On the other hand, since an output of a signal having a large signal width is less affected by distortion, a normal signal 21 can be output.
Thus, as the number of pixels used in an image sensor increases, the amount of data to be processed increases, and a global signal may be distorted due to image signals having a large signal width. This distortion of a global signal may eventually appear as noise of an image sensor.